Individual Differences.pdf

Individual Differences 09 October 2023 14:58 Main Ideas Medical disorders Psychiatric disorders Personality and Cognition Notes Twin studies can indicate the degree to which genetic and environmental influences contribute to the onset of medical disorders and other traits Meta-analysis of the herita...

Individual Differences 09 October 2023 14:58 Main Ideas Medical disorders Psychiatric disorders Personality and Cognition Notes Twin studies can indicate the degree to which genetic and environmental influences contribute to the onset of medical disorders and other traits Meta-analysis of the heritability of human traits based on 50 years of twin studies (Polderman et al.) found an aspect of heritability in many traits Environments are not just a passive background, we can control and actively co-create an environment through our social relationships for example Example of how genetically informative research can change understandings about condition and challenge assumptions: ○ Autism - 'Refrigerator Mother' hypothesis claimed that autism is a result of the mother not being emotionally available to the child ○ Most measures of social environment are partly heritable Heritability ○ a measure of the extent to which differences in people's genes account for differences in their traits ○ Heritability estimate derived from e.g. twin studies, is the sum total of all genetic variation ○ Includes ‘de novo’ mutations – i.e. genetic effects that are not necessarily inherited from parents ○ Estimates do not apply to a single individual ○ High heritability estimates do not imply that behaviour is genetically pre-determined ○ h2 estimates apply to a particular population at a particular time ○ The genes of a trait do not change in the population but the degree to which they account for individual differences do The genetic estimates from twin models represent any and all genes that explain why , for example, some individuals are more prone to depression than others Specific genes that account for variation in the phenotype are not identified in the twin models Molecular Genetics Twin/adoption studies are not aimed at identifying/studying specific genes It is important to establish in these studies: ○ The degree to which a trait/disorder is heritable ○ whether the genetic effects are unique to the disorder or shared with other disorders ○ whether genetic effects are stable throughout development Molecular genetic studies of behaviour and psychiatric illness attempt to understand the specific genetic influences on a trait/disorder Normally compares genotypes of individuals with and without disorder Older studies focused on candidate genes Newer studies ‘comb’ through the whole genome ○ Genome Wide Association Studies ○ Sequencing Genome ‘Genome’ = 3 billion DNA base pairs ○ > 99% identical for all people ○ > 1% contains differences that account for individual differences in physical attributes, ability, psychiatric risk etc. (Polymorphic genes) Genome has start and stop signals (codons) to define a gene Non-coding DNA is important because the transcribed RNA regulates gene expression Alleles or genes may increase likelihood of one behaviour/disorder, but decrease likelihood of another. ○ This means the risk of having a specific gene is probabilistic (might be considered an advantage under one circumstance or a risk in another) Types of genetic variation Large scale ○ Chromosomal abnormalities ○ Change in the number of chromosomes (whole) ○ Change in the arrangement chromosomes (part) Medium scale ○ Copy number variation (CNVs), insertions/deletions Small scale ○ Single base change (SNPs) Single nucleotide polymorphism (SNP) Single base change 2 alleles = C + T Can be heterozygote or homozygote (CC, CT, TT) Variations in the genome (such as a single nucleotide polymorphism – SNP) are found about every 1000th base pair These polymorphisms account for much of individual differences in the risk for psychiatric disorders Psychiatric genetics Polygenic, heterogeneous disorders ○ Generally weak risk effects of a single genotype across the population Summary Both genetic and environmental influences are important for most disorders and dimensions Heritability is a measure of the extent to which differences in people's genes (both inherited from parents, and ‘de novo’ mutations) account for differences in their traits Heritability statistic applies to a particular population, at a particular time Molecular genetic studies of psychiatric disorders and traits have produced very few ‘big hits’ Genetic effects small and probabilistic, most studies lack sufficient power to detect such effects Genetic effects may be conditional on environmental risk exposure PSYC0036 Genes and Behaviour Page 1